Why does rendering nothing take 45 seconds?
It is not a big surprise.

This is the time it takes to render nothing on an old i7 2600K processor:



And this is the time it takes to render the same nothing on the same old i7 2600K processor 2048 times(2048 samples):



Cycles is not very adaptive. It does not care much that it is the same plain color you ask to be sampled 128 times. It will do precisely that. This is pretty normal. The GPU you are using might not be a very powerfull solution for rendering. You could try CPU rendering as well see if that is any better with the CPU you have. 

If you need simple results, you could also look into OpenGL rendering. That will render whatever you see in the viewport. It has a few settings so you could use better antialiasing as well.